Fuser systems for printers, copiers and like devices are typically designed to receive an AC line voltage falling within a narrow voltage range, e.g., 90 VAC to about 110 VAC, typical in Japan, 100 VAC to about 127 VAC, typical in the U.S., and 200 VAC to about 240 VAC, also typical in the U.S. and Europe as well. It would be desirable from a device distribution standpoint to have a universal fuser heating apparatus forming part of a fuser subassembly capable of working in each of these AC line voltage ranges so that fewer unique printer, or copier models would be needed for distribution.
U.S. Pat. No. 5,483,149 discloses a fuser control system, which permits a fuser having a lamp designed for a very narrow AC line voltage range to be used over a wide range of AC line voltages. The '149 patent teaches determining a ratio of the rated power for the fuser lamp to an amount of power available based on the input AC line voltage and the resistance of the fuser lamp. A control signal for controlling the operation of a zero-crossing switch is generated having a duty cycle substantially equal to the determined ratio. The zero crossing switch, in accordance with the control signal, provides half cycles of an AC power signal to the fuser lamp. Hence, average power dissipated by the lamp is maintained at a level substantially equal to the rated power level for the fuser lamp by allowing only a portion of the available AC power signal to be provided to the lamp. Where fuser lamps designed for low AC line voltages and, hence, having low resistances, are used with high input AC line voltage, the average power dissipated by the fuser lamps is maintained at a desirable level by defining low duty cycles of the high AC line voltage. Unfortunately, the fuser lamps so actuated result in high current levels, which oftentimes create unacceptable flicker problems.
Accordingly, there is a need for an improved universal fuser heating apparatus capable of working over low and high AC line voltage ranges, which does not cause unacceptable flicker problems.